An exhaust gas heat exchanger for performing heat exchange between exhaust gas generated by a liquid cooled internal combustion engine and liquid coolant used for cooling the engine is well known, for example, as disclosed in Japanese Patent Publication No. 2000-97578. FIG. 16 is a schematic vertical cross sectional view showing an assembly configuration of the exhaust gas heat exchanger shown in the above Japanese Patent Publication. A heat exchange core 140 has a plurality of laminated tubes 130 forming exhaust gas passages 132, through which exhaust gas flows. A first tank member 155 having a first insertion opening 157 and a second tank member 156 having a plurality of second insertion openings 158 are sequentially assembled to end portions of the laminated tubes 130. Such an assembled unit is brazed to finish a heat exchanger body 170 having tank portions 152 formed at both sides of the laminated tubes 130.
Though a left tank portion is omitted in FIGS. 16 and 17, the left tank portion employs symmetrically the same configuration to the right tank portion. FIG. 17 is a partial cross sectional view explaining a flow path in the exhaust gas heat exchanger in FIG. 16. Exhaust gases which flow into the second tank member 156 are distributed to plural exhaust gas passages 132 and flow to the left side in the drawing. Cooling liquid which flows into the tank portions 152 through an inlet pipe 151 is distributed and delivered to coolant passages 131, which are formed between the tubes 130 by projections 133 provided at both edges of the tubes 130. The cooling liquid flows to the left side in the drawing, so that heat exchange is carried out with the exhaust gases flowing in parallel therewith.
The above conventional art, however, has a problem that efficiency of heat exchange can not be easily increased due to a parallel flow, in which exhaust gas flowing inside the tubes 130 and liquid coolant flowing outside the tubes 130 (between the tubes 130) flow in the same direction. It is another disadvantage in that the heat exchanger becomes longer in its size, because two tank portions 152 are necessary at both ends of the tubes 130 for distributing the coolant into and collecting the coolant from the multiple tubes.
A direction of assembling the tank members 155 and 156 at both ends of the tubes 130 is at a right angle to a direction of laminating the tubes 130. Accordingly, a problem of cost increase is unavoidable due to this difficult assembling. It is, furthermore, necessary to control a distance between the laminated tubes 130 as well as a distance between the multiple second insertion openings 158 to be formed at the second tank member 156, at an optimum amount, in order not to make in-process brazing defects, which might occur in a brazing process subsequent to assembling, at brazed portions between the tubes 130 and at brazed portions between the tubes 130 and the second insertion openings 158.